Printing Both Matching and Non-Matching Patterns - regex

Question

I am trying to compare two files to then return one of the files columns upon a match. The code that I am using right now is excluding non-matching patterns and just printed out matching patterns. I need to print all results, both matching and non-matching, using grep.
File 1:
A,42.4,-72.2
B,47.2,-75.9
Z,38.3,-70.7
C,41.7,-95.2
File 2:
F
A
B
Z
C
P
E
Current Result:
A,42.4,-72.2
B,47.2,-75.9
Z,38.3,-70.7
C,41.7,-95.2
Expected Result:
F
A,42.4,-72.2
B,47.2,-75.9
Z,38.3,-70.7
C,41.7,-95.2
P
E
Bash Code:
while IFS=',' read point lat lon; do
check=`grep "${point} /home/aaron/file2 | awk '{print $1}'`
echo "${check},${lat},${lon}"
done < /home/aaron/file1

Answer 1

In awk:
$ awk -F, 'NR==FNR{a[$1]=$0;next}{print ($1 in a?a[$1]:$1)}' file1 file2
F
A,42.4,-72.2
B,47.2,-75.9
Z,38.3,-70.7
C,41.7,-95.2
P
E
Explained:
$ awk -F, ' # field separator to ,
NR==FNR { # file1
a[$1]=$0 # hash record to a, use field 1 as key
next
}
{
print ($1 in a?a[$1]:$1) # print match if found, else nonmatch
}
' file1 file2

Answer 2

If you don't care about order, there's a join binary in GNU coreutils that does just what you need :
$sort file1 > sortedFile1
$sort file2 > sortedFile2
$join -t, -a 2 sortedFile1 sortedFile2
A,42.4,-72.2
B,47.2,-75.9
C,41.7,-95.2
E
F
P
Z,38.3,-70.7
It relies on files being sorted and will not work otherwise.
Now will you please get out of my /home/ ?

Answer 3

another join based solution preserving the order
f() { nl -nln -s, -w1 "$1" | sort -t, -k2; }; join -t, -j2 -a2 <(f file1) <(f file2) |
sort -t, -k2 |
cut -d, -f2 --complement
F
A,42.4,-72.2,2
B,47.2,-75.9,3
Z,38.3,-70.7,4
C,41.7,-95.2,5
P
E
Cannot beat the awk solution but another alternative utilizing unix toolchain based on decorate-undecorate pattern.

Answer 4

Problems with your current solution:
1. You are missing a double-quote in grep "${point} /home/aaron/file2.
2. You should start with the other file for printing all lines in that file
while IFS=',' read point; do
echo "${point}$(grep "${point}" /home/aaron/file1 | sed 's/[^,]*,/,/')"
done < /home/aaron/file2
3. The grep can give more than one result. Which one do you want (head -1) ?
An improvement would be
while IFS=',' read point; do
echo "${point}$(grep "^${point}," /home/aaron/file1 | sed -n '1s/[^,]*,/,/p')"
done < /home/aaron/file2
4. Using while is the wrong approach.
For small files it wil get the work done, but you will get stuck with larger files. The reason is that you will call grep for each line in file2, reading file1 a lot of times.
Better is using awk or some other solution.
Another solution is using sed with the output of another sed command:
sed -r 's#([^,]*),(.*)#s/^\1$/\1,\2/#' /home/aaron/file1
This will give commands for the second sed.
sed -f <(sed -r 's#([^,]*),(.*)#s/^\1$/\1,\2/#' /home/aaron/file1) /home/aaron/file2